1. Field of the Invention
The present invention relates to a power supply device using a magneto alternating current (AC) generator.
2. Description of the Related Art
As a power supply device, there is conventionally known, for example, a power supply device using a magneto AC generator disclosed in each of Japanese Patent No. 4100793, Japanese Utility Model Registration No. 2076397, and Japanese Utility Model Registration No. 2530219. Such power supply device generally includes a magneto AC generator, a rectifier circuit, and a generated voltage control circuit. Electric power generated by the magneto AC generator is converted into a direct current (DC) by the rectifier circuit, and then input to the generated voltage control circuit. The generated voltage control circuit performs short-circuit control or opening control so as to obtain a voltage in accordance with a voltage of an electrical load formed of, for example, an electrical storage device, and then the electric power is supplied to the electrical load.
In the conventional power supply device using the magneto AC generator, the opening control and the short-circuit control are independently controlled as voltage control. Input torque to a rotor of the magneto AC generator from a torque supplying device (engine in a case of automobile), which supplies torque to the rotor, differs depending on rpm of the rotor. For this reason, the generator of the conventional power supply device does not necessarily generate power with input torque most suitable for an operating state of the rotor or the torque supplying device.
Further, during an opening operation, a no-load induced voltage is generated at an output end of the magneto AC generator. The no-load induced voltage is proportional to the rpm of the rotor, and becomes the maximum at the actual maximum rpm. Therefore, the power supply device including the magneto AC generator needs to be designed in terms of withstand voltage in expectation of the no-load induced voltage generated at the actual maximum rpm. For this reason, an element with high withstand voltage must be selected, which leads to an increased size and cost of the power supply device. In recent years, the magneto AC generator has a tendency to increase its output, and hence the no-load induced voltage generated in the magneto AC generator is becoming increasingly larger, which requires the design for higher withstand voltage.